Regulated power supply



July 13, 1 E. R. M NULTY ET A].

REGULATED POWER SUPPLY Filed Dec. 21, 1962 FIG. 20

FIG.2b

FIG. 2e

- -V INPUT FIG. 2

VUV- 1' T2 lNVENTORS EDWARD R. MC NULTY ED RD A. $0M) BY &-;-

m RNE United States Patent 3,195,036 REGULATED POWER SUPPLY Edward R.McNuity, Saugerties, and Edward A. Menard,

Ruby, N.Y., assignors to International Business Machines Corporation,New York, N311, a corporation of New York Filed Dec. 21, 1962, Ser. No.246,530 2 (llairns. (Q1. Mi -16) The present invention relates to apower supply which furnishes direct current to a load at regulatedvoltage, and particularly to such a supply in which in-phase pulsatingcurrent is delivered at first and second source taps, at first andsecond higher voltages, respectively. in the contemplated supply, onetap at a time is to be selectively connected to the lead in accordancewith the voltage requirement-s of the load.

In the past, tap changing regulators of the type mentioned above havebeen provided in which electromechanical switching gear has been used toeifect selective connection between any of multiple taps and a load.Such gear has the inherent disadvantages of being bulky, slow, andrelatively expensive. While other tap changing regulators have beenprovided in which non-mechanical apparatus is used to effect theswitching function, such apparatus usually has the inherent disadvantageof being both complex and expensive.

Accordingly, it is an object of the present invention to provide a newand improved direct current supply.

Another object of the present invention is to provide an improvedcurrent supply of the tap changing type wherein the voltage deliveredmay be changed by simple and easily controlled components.

Another object of the present invention is to provide a tap changingregulator for furnishing voltage at various levels without resorting tothe use of electro-mechanical devices.

Another object of the present invention is to provide a new and improvedpower supply of the tap changing type which employs controlledrectifiers as switching elements wherein advantage is taken of theinherent ability of unidirectionally conductive devices to becomenonconductive when back-bi.ased.

' The foregoing and other objects, features, and advantages of theinvention will be apparent from the following,

more particular description of a preferred embodiment of the inventionas illustrated in the accompanying drawings.

In the drawings:

FIG. 1 represents a schematic diagram of the preferred embodiment of aregulated, tap changing direct current power supply;

FIGS. 2A through 2E represent voltages at various points in the system,hereinafter described, with respect to a common time base.

Turning to FIG. 1, there is shown transformer 1 having a primary winding1A which is connected to an alternating current source (not shown). Thealternating current source produces a square wave voltage ofsubstantially uniform amplitude (level) and frequency represented inFIG. 2A. In the following description, it is assumed that there issubstantially no variation in input voltage amplitude with changes inthe amount of power passed through transformer 1.

Secondary winding 1B of transformer 1 has a center tap 2A as well as afirst pair of taps, 2B and 2C, which are balanced with respect to tap2A, so that transformer 1 delivers at taps 2B and 2C a signal having asubstantially square wave voltage in which the positive andnegative-going excursions about a reference potential at tap 2A aresubstantially identical. The amplitude of the positive-going voltageexcursions at taps 2B and 20 with respect to tap 2A is represented inFIG. 2D. A second pair of taps, 2D and 2E is provided on secondarywinding 1B, taps 2D and 2E also being balanced with respect to centertap 2A and delivering substantially square wave output voltage at asecond level that is substantially in-phase with, but at a voltagehigher than that delivered at taps 2B and 2C. The amplitude of thepositive-going excursions at taps 2D and 2E with respect to tap 2A isrepresented in FIG. 2B. For reasons that are to be made apparent, eachof taps 213 through 2E is to be regarded as a source of voltage pulseswhich are positive-going with respect to tap 2A when observed duringappropriate, alternate cycle halves of the output signal developedacross winding 113. Such power pulses from selected pairs of secondarywinding 13 taps are to be delivered to load 3 by means hereinafterdescribed.

Load 3 has input terminals of 3A and SE to which current fromtransformer 1 is delivered. The nature of load 3 is such that it usespower in varying amounts, and that power is to be delivered to terminals3A and 3B at a voltage only slightly below a predetermined minimumvalue, indicated as V in FIG. 2B, which represents the voltage deliveredat terminals 3A and 3B. The value of V is slightly less than the voltageamplitude indicated in FIG. 2D. If it is assumed for the moment: (1)that only taps 2B and 2C are connected to terminal 3A and 3B by diodes6A and 6B in full wave rectifier configuration, (2) that power normallyis being delivered at a fixed rate to load 3; and (3) that an increasedamount of power is consumed by load 3 between times T1 and T2, indicatedon the time of axis of FIG. 2B, then it follows that between times TIand T2, the voltage at terminals 3A and 33 would decrease and might dropsubstantially below the value V in the manner represented by the dottedportion of the curve indicated as V in FIG. 2B. In order to minimizeexcursions of voltage at terminals 3A and 3B below V the next describedmeans is provided to couple tap 2A and a selected pair of taps ZB-ZC and2D-2E to terminals 3A and 3B. The last named means includes filter 4,which may be of any of a number of conventional, commercially availabletypes which have metallic paths indicated in the drawing by dotted lineswhich serially connect conductors 5 and 7 to terminals 3B and 3A,respectively.

In the contemplated configuration, the means coupling theabove-identified pair of tap sources 2B-2C as well as tap 2A acrossconductor 5 and 7 (and hence across terminals 3A and 313) comprises afirst pair of unidirectionally conductive devices, such as diodes 6A and6B, serially connected in full wave rectifier configuration between tap2B and conductor 7 and between tap 2C and conductor 7, respectively(i.e., the diodes are poled to be conductive during the positive goinghalves of signals appearing at taps 2B and 2C). Diodes 6A and 6B are ofthe dry plate type, and are normally (i.e., in the absence of aback-biasing potential which maintains the cathode positive with respectto the anode) effective to conduct current in the forward direction,i.e., from anode to cathode during the time that taps 2C and 2D arepositive with respect to tap 2A. Consequently, power normally isdelivered by diodes 6A and 6B via conductor 7 to tap 3A of load 3 andreturned via conductor 5 and tap 2A at a voltage observed at terminal 3Awhich is positive with respect to terminal 3B and ground potential.

The above mentioned means also includes a pair of controllable,unidirectionally conductive devices, i.e., controlled reoti-fie-rs 8 and9, which may be of any commercially available type. The main anodes ofrectifiers 8 and 9 are connected to taps 2D and 2E While the cathodesare connected to conductor 7. It is to be seen that means is providedfor establishing a metallic path which connects the cathodes ofrectifiers 8 and 9 in parallel with' aneaoae 3 the cathodes of diodes 6Aand 6B. Thus rectifiers 8 and 9 serve as switches, and when operativei.e., conductive, serve to connect source taps 2D 2 E and tap 2A to loadinput terminals 3A and 3B in the same manner that diodes dA-dB connecttaps ZB-ZC to the load terminals.

Controlled rectifiers S and 9 have starting anodes or control electrodes8A and 9A, respectively, and each becomes conductive in the forwarddirection when both its main anode and starting anode become positivewith re spect to its cathode. Once rendered conductive, each ofrectifiers 8 and 9 remains conductive until its cathode becomes positivewith respect to its anode.

Control electrodes 8A and 9A are connected together and to inputconductor 1-2 which normally is maintained by sensing means 169 at avoltage less positive than the average voltage produced at taps 2B and2C, sensing means being hereinafter described. It is assumed for themoment that means 11 also is operable to produce ou conductor 12 asignal which is more positive with respect to the above mentionednorm-a1 signal and the voltage contributed to conductor 7 from taps 2Band 2C, so that the latter signal makes control electrodes 8A and 9Apositive with respect toconductor 7 and to the cathodes of rectifiers 8and 9. With this arrangement, rectifiers 3 and 9 normally are maintainedin nonoonduc-t-ive state and are selectively made operative upon theappearance of the above described positive signal on conductor 12.

Sensing means 10 produces a continuing, positive-going signal on itsoutput conductor 12 in response to the re duction in voltage applied toits input terminals 11A and 11B belowa predetermined minimum. Therelationship is tobe seen by comparing FIG 2C (which shows the voltagepresent on conductor 12) to FIG. 2B. While means 16 may be chosen fromany of a number of commonly available designs, for purposes ofillustrating the present invention the configuration of apparatus shownin FIG. 1 is preferred. Input terminals 11A. and 11B are connecteddirectly to terminals 3A and 3B, respec tively. Voltage appearing acrossthe input terminals of load 3 therefore is applied to theemitter-collector circuit of NPN type transistors and via resistors 13and 2%, respectively, and via common zener diode 14, which serves toclamp the emitters of transistors 15 and 29 at a fixed positive voltagewith respect to terminals 11B and 3B. A dropping circuit is placedacross terminals 11A and 11B and includes zener diode 16 andpotentiometer 17. The tap of potentiometer 17 is coupled via resistor tothe base of transistor 15. When the voltage applied to terminals 11A and11B is greater than the above mentioned voltage V diode 16 isconductive, and the resulting voltage at the base of transistor 15 issufficiently positive with respect to its emitter to hold transistor 15in a saturated state. As a consequence of the saturation of transistor15, the collector thereof, as well as the base of transistor 20 (whichis connected to the transistor 15 collector via resistor 18 and diode19) are maintained substantially at the voltage present on the emitterof transistor 20: i.e., at the voltage developed across clamping diode14. At this voltage across the base and emitter of transistor 20,transistor 20 is maintained in its cutoff state, so that substantiallyno current flows in its emitter-collector circuit. Consequently, thevoltage present at the collector of transistor 21 and the base of NPNtype transistor 21 (which is directly coupled to the collector oftransistor 20) are maintained at a voltage which is positive withrespect to ground and to the emitter of transistor 21 and whichapproaches the value of the voltage present on terminal 3A. Theemitter-collector circuit of transistor 21 is connected across thevoltage source +V and diode 1 1 via resistor 23 and emitter-followerresistor 24. With the base of transistor 21 maintained positive withrespect to its emitter, transistor 21 is driven into saturation. As aresult, the collector of transistor 21 is maintained at relatively lowpositive voltage with respect to the terminal 3B (which,

it will be recalled, is at ground potential). Since output conductor 12is directly connected to the collector of transistor 21, the voltagepresent on conductor 12 normally is maintained slightly positive withrespect to ground and more negative than the average voltage appearingon conductors 7.

When the voltage present at terminals 3A and 3B, and consequentlyterminals 11A and 11B, drops below the predetermined positive value VZener diode 16 becomes nonconductive, therewith allowing the voltageapplied to the base of transistor 15 to become sufiiciently negativewith respect to the emitter of transistor 15 to drive transistor 15beyond cutoff. As a consequence, transistor 15 substantially stopsconducting current through its emitter-collector circuit and allows thevoltage at the base of transistor 21% to become positive with respect toits emitter to the point where transistor 29 goes into saturation. Asthe result of driving transistor 20 into saturation, the collectorthereof as well as the base of transistor 21 become sufiicientlynegative with respect to the emitter of transistor 21 to drivetransistor 21 beyond cutoif. Transistor 21 at this time ceases toconduct in its emitter-collector circuit, so that voltage appearing onoutput condoctor 12 becomes positive and approaches the value of source+V. Should the voltage across terminals 11A and 11B later rise to avalue greater than V transistor 15 is again driven into saturation,therewith making transistor 21) eifective to make transistor 21conductive in its emitter-collector circuit in the above describedmanner. The value of the more positive signal on conductor 12 is ofsufiicient amplitude to make control electrodes 8A and 9A positive withrespect to the voltage present on conductor 7 and therewith rendersrectifiers 8 and 9 operative to conduct current.

From the foregoing description it is to be seen that during the time thenormal-signal is present on conductor 12, controlled rectifiers S and 9are maintained nonconductive, so that diodes 6A and 63 pass current toload 3 at a voltage sufiicient to maintain input terminal 3A at apositive voltage with respect to 3B which is greater than V However, asthe power requirements of load 3 increase (as at time T1) to the pointwhere the voltage at terminal 3A would with respect to terminal 33 dropto a value less than V sensing means 10 becomes effective to produce theabove-described more-positive signal to conductor 12 and to controlelectrodes 8A and 9A. Consequently, each of rectifiers 8 and 9 isrendered conductive as taps 2D and 2E, respectively, become positivewith respect to tap 2A. Since the voltage delivered at taps 2D and 2B isin phase with and at voltage substantially higher than the voltagedelivered at taps 2B and 2C, the voltage appearing at the cathodes ofrectifiers 8 and 9 during the intervals that those rectifiers areconductive is substantially higher than the voltage delivered to theanodes of diodes 6A and 6B. Therefore, diodes 6A and 6B are back-biased(hence, nonconductive) during the periods that rectifiers 8 and 9 areconductive.

This relationship is to be seen by comparing FIGS. 2D

and 2E, which represent the voltage of power pulses supplied toconductor '7 via diodes 6A-6B and via rectifiers 8-1, respectively.

Referring to FIGS. 2B through 2E, if it is assumed for the moment thatthe voltage at terminal 3A-3B has dropped slightly below the V (owing toan increased demand for power within load 3) at time T1 and that sens"ing means 10 has thereupon generated a positive signal on conductor 12(represented in FIG. 3C), then the one of rectifiers 8 and 9 connectedto the currently-positive one of taps 2D and 2E becomes conductive,therewith back-biasing and rendering nonconductive the one of diodes 6Aand 6B which is connected to the currentlypositive one of taps 2B and2C. Consequently, power at the higher voltage delivered at taps 2D and2E is' applied across terminals 3A and 3B of load 3, and power from taps2B and 2C is shut ofi upon the back-biasing of diodes 6A and 63. Currentcontinues to how alternately through rectifiers 3 and 9 during the timethat the positive signal is maintained on conductor 12. It is assumedthat at time T2 the power requirement of load 3 decreases, so that thevoltage across terminals 3A and 33 returns to a value greater than VConsequently, sensing means replaces the more positive signal onconductor 12 with the normal level signal. Upon removal of the morepositive signal from conductor 12, the currently-conducting one ofrectifiers 8 and 9 remains operative and continues to pass current toconductor 7 until the voltage applied to the main anode thereof becomesnegative with respect to its cathode. Thereupon the back-biasing voltageis removed from diodes 6A and 68, so that upon the occurrence of thenext positive going signal on one of taps 2B and 2C, the appropriate oneof diodes 6A and 63 again becomes conductive. Thereafter, diodes 6A and6B supply power to load 3 until sensing means 10 again applies the lowvoltage-indicating signal to conductor 12 with the above noted effects.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it Will be understood bythose skilled in the art that various changes in form and details may bemade variant without departing from the spirit and scope of theinvention.

What is claimed is:

1. In a supply to deliver direct current to first and second inputterminals of a load,

a transformer having a primary winding coupled to an alternating currentsource and a secondary winding,

said secondary Winding having a common return tap as well as first andsecond taps to furnish current of like polarity and phase at a firstvoltage and a second, higher voltage, respectively,

means to directly connect said common tap to said first load terminaland to directly connect said first and said second transformer taps tosaid second load terminal,

said means including a diode serially connected between said first tapand said second load terminal normally efiective to conduct currenttherethrough in a forward direction to said load,

said means also including a rectifier having a control anode, meansconnected across said load terminals effective in response to thereduction of voltage thereat below a predetermined value to apply asignal to said control anode, i

said rectifier being serially connected between said second transformertap and said second load terminal and effective upon the application ofa signal to said electrode to conduct current therethrou-gh in the samedirection with respect to said load as said diode,

said rectifier being etfective in conductive state to provide current tosaid load,

and means coupling said rectifier to said diode to apply reverse voltageto said first diode during the time said rectifier is conductingcurrent.

2. In a supply to deliver direct current to first and second inputterminals of a load,

a transformer having a primary winding coupled to an alternating currentsource and a secondary winding,

said secondary winding having a center tap as well as first and secondpairs of taps, said taps in each of said pairs being disposed onopposing sides of and :being balanced with respect to said center tap,

first and said second pairs of taps being disposed to deliver current ata first voltage and at a second, higher voltage, respectively,

means connecting said center tap to said first load terminal to form acommon return path to said transtt'or-mer secondary winding,

means comprising a pair of diodes connected in series between said firstpair taps and said second load terminal poled to form a path to conductcurrent in a fixed direction from said first pair taps to said secondload terminal during alternate halves of said voltage cycle produced insaid secondary Winding by said source,

means comprising a pair of controlled rectifiers, each of saidrectifiers having a main anode and a cathode connected in series betweensaid second pair of taps and said second load terminal and also having acontrol anode,

means connected across said load input taps effective in response to thereduction of voltage thereat below a predetermined value to apply asignal to said control anodes,

said controlled rectifiers being responsive upon the application of asignal to said control anodes thereat to conduct current from said mainanode to said cathode in a forward direction in the same direction withrespect to said load as said diodes from said second pair of taps tosaid load,

and means coupling said rectifiers to said diodes to apply reversevoltage to said first pair diodes during the time said rectifiers areconductive.

References Cited by the Examiner UNITED STATES PATENTS 2,959,726 11/60Jensen 323-435 3,040,239 6/62 Walker 323-435 3,082,369 3/63 Landis.

3,141,124 7/64 Atherton.

LLOYD MCCOLLUM, Primary Examiner.

1. IN A SUPPLY TO DELIVER DIRECT CURRENT TO FIRST AND SECOND INPUTTERMINALS OF A LOAD, A TRANSFORMER HAVING A PRIMARY WINDING COUPLED TOAN ALTERNATING CURENT SOURCE AND A SECONDARY WINDING, SAID SECONDARYWINDING HAVING A COMMON RETURN TAP AS WELL AS FIRST AND SECOND TAPS TOFURNISH CURRENT OF LIKE POLARITY AND PHASE AT A FIRST VOLTAGE AND ASECOND, HIGHER VOLTAGE, RESPECTIVELY. MEANS TO DIRECTLY CONNECT SAIDCOMMON TAP TO SAID FIRST LOAD TERMINAL AND TO DIRECTLY CONNECT SAIDFIRST AND SAID SECOND TRANSFORMER TAPS TO SAID SECOND LOAD TERMINAL,SAID MEANS INCLUDING A DIODE SERIALLY CONNECTED BETWEEN SAID FIRST TAPAND SAID SECOND LOAD TERMINAL NORMALLY EFFECTIVE TO CONDUCT CURRENTTHERETHROUGH IN A FORWARD DIRECTION TO SAID LOAD, SAID MEANS ALSOINCLUDING A RECTIFIER HAVING A CONTROL ANODE, MEANS CONNECTED ACROSSSAID LOAD TERMINALS EFFECTIVE IN RESPONSE TO THE REDUCTION OF VOLTAGETHEREAT BELOW A PREDETERMINED VALUE TO APPLY A SIGNAL TO SAID CONTROANODE, SAID RECTIFIER BEING SERIALLY CONNECTED BETWEEN SAID SECONDTRANSFORMER TAP AND SAID SECOND LOAD TERMINAL AND EFFECTIVE UPON THEAPPLICATION OF A SIGNAL TO SAID ELECTRODE TO CONDUCT CURRENTTHERETHROUGH IN THE SAME DIRECTION WITH RESPECT TO SAID LOAD AS SAIDDIODE, SAID RECTIFIER BEING EFFECTIVE IN CONDUCTIVE STATE TO PROVIDECURRENT TO SAID LOAD, AND MEANS COUPLING SAID RECTIFIER TO SAID DIODE TOAPPLY REVERSE VOLTAGE TO SAID FIRST DIODE DURING THE TIME SAID RECTIFIERIN CONDUCTING CURRENT.